On a coordinated installation, the power cabling and the ELV cabling (data, CCTV, fire alarm, public address, access control, building controls) are kept on separate runs. It isn't habit or tidiness; there are two solid engineering reasons, and the wiring code puts a rule behind them. Here is the why, what the standards actually ask for, and how it is handled on site.
Reason one, interference
A power cable carries alternating current at 50 Hz, with harmonics and switching transients on top, and that current sets up a changing magnetic field around the cable. An ELV signal cable run close and parallel to it sits inside that field and picks up an induced voltage, electrical noise the signal system never generated and cannot fully reject. On the ELV side it shows up as data errors and retransmissions, artefacts on a camera feed, hum on an audio line, or a spurious state on a control or fire-alarm circuit.
The coupling grows with the current in the power cable and with the length the two run side by side, and it falls off quickly as they move apart. So two levers control it: distance, and screening (screened cable and bonded metal containment).
Reason two: safety
ELV systems are treated as safe to touch, often SELV, where the low voltage is itself the safety barrier at every handset, camera, reader and panel a person contacts. If a power conductor sharing the same conduit has its insulation compromised and makes contact with an ELV conductor, that whole ELV system can be raised toward LV potential, quietly defeating the assumption it was built on. Keeping the bands apart preserves the integrity of the safe-voltage classification, end to end.
What the code asks for, voltage bands
IS 732, the Indian wiring code (its 2019 revision aligned with IEC 60364), classifies circuits into voltage bands: Band I covers ELV, signal, data, control, alarm, telecom, and Band II covers LV power at 230 / 415 V. The rule that follows is straightforward, circuits of different bands should not share the same wiring system (the same conduit, trunking or multicore cable) unless:
- every conductor is insulated for the highest voltage present; or
- the bands are separated, by a partition, an earthed metal screen, or a separate conduit / trunking compartment.
(The international parent is IEC 60364-5-52, on the selection and erection of wiring systems.) Fire-alarm wiring carries its own segregation requirement on top of this, under IS 2189 and the National Building Code, so that interference from a power circuit can neither raise a false alarm nor mask a real one.
How far apart, the separation distances
The wiring code sets the principle; the actual separation distances for data cabling come from the structured-cabling standards: EN 50174-2 and TIA-569 / BICSI. As a guide, EN 50174-2 starts at around 200 mm between unscreened power and unscreened data, and reduces toward zero as screening is added on either side and the cables sit in bonded metal containment. The exact figure turns on three things: the parallel run length, the size of the power circuit, and the screening on both the power and the ELV side. The more screening and proper containment you have, the less air gap you need.
On site
In practice the rule resolves to a handful of habits:
- Separate containment. ELV in its own conduit, tray or trunking, or, where a single tray is shared, a partition with an earthed metal divider between the bands.
- Hold the distance on long parallel runs, and where power and ELV must cross, cross at right angles, the orientation that couples the least.
- Bond the metal containment properly, so a screened tray actually does its screening job.
- Size the ELV power in from the start, the UPS-backed and supervised feeds for the NVR, the server and the fire-alarm panel belong in the LT-panel design from day one, not retrofitted later.
None of it is difficult; it just has to be decided at the drawing stage, because separating cables that have already been pulled in together is far harder than routing them apart in the first place.
What we do
Shreetuvis designs and installs the ELV stack, CCTV, fire alarm, access control, public address and structured cabling, together with the electrical scope, by the same engineering team. So the band segregation, the containment and the UPS-backed feeds are coordinated from the drawing stage and held to the same standard as the wiring itself. See ELV systems for the range, and good wiring workmanship for the site habits this sits alongside.